Computer power supply

ABSTRACT

An object of the present invention is to provide a computer power supply in which, by improving the circuit itself, internal heat loss can be reduced, thereby greatly improving efficiency. A partial resonance circuit  8  is constituted by a primary side winding N 1  of a high frequency transformer  3,  a resonance condenser  7,  and two switching elements Q 1,  Q 2,  a secondary side output circuit  4  for driving a load is connected to a secondary side of the high frequency transformer  3  via a winding, and a reverse converter  11  for driving and halting the first switching element and second switching element by causing the respective phases thereof to differ on the basis of a driving signal is provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a computer power supply fordriving various loads using, for example, a DC output followingrectification by an AC side power circuit of an AC voltage from acommercial AC power supply or a DC voltage from a DC power supply suchas a battery or secondary battery.

[0003] 2. Description of the Related Art

[0004] When a switching power supply with a high output capacitance (200to 300W) is provided in a 1U (height 44 mm units) size as the computerpower supply described above, a large number of cooling fans are usedconventionally in order to extract an output capacitance of 210W or moredue to the small size, and in so doing decreases in efficiency due tointernal heat loss can be avoided. In many cases, however, efficiency ofonly 65% to 68% or thereabouts can be achieved, and moreover, powerconsumption increases as the number of cooling fans rises. As a result,considerable increases in efficiency cannot be achieved, andimprovements are urgently desired.

[0005] A device which is constituted such that the internal temperatureis maintained at a constant level at all times by modifying thedischarge rate of the cooling fan in accordance with the amount ofgenerated heat, which varies according to the load current, has alsobeen proposed (see Japanese Unexamined Patent Application Publication7-231058 (FIG. 1), for example).

[0006] In the aforementioned publication, the discharge rate of thecooling fan is reduced when the load current is small, and thusefficiency can be improved slightly in comparison with a device in whicha large number of cooling fans are all driven. However, this device doesnot provide an ultimate solution.

SUMMARY OF THE INVENTION

[0007] The present invention has been designed in consideration of thesituation described above, and it is an object thereof to provide acomputer power supply in which efficiency is improved greatly byimproving the circuit itself such that internal heat loss itself isreduced.

[0008] In order to solve the aforementioned problem, a computer powersupply of the present invention is such that a first switching elementand a second switching element operating with a DC voltage as an inputare disposed on the primary side of a high-frequency transformer in astate of differing polarities, the first switching element is connectedto one end of a primary side winding of the high-frequency transformer,and the second switching element is connected to the same end of theprimary side winding as the connection side of the first switchingelement via a resonance condenser, whereby the primary side winding,resonance condenser, and two switching elements constitute a partialresonance circuit. A secondary side output circuit for driving a load isconnected to the secondary side of the high-frequency transformer via awinding, a first driving circuit and a second driving circuit having adelay element are provided for driving and halting the first switchingelement and second switching element on the basis of a driving signal bycausing the respective phases thereof to differ, and a reverse converteris provided for supplying to the input portion of one of the drivingcircuits insulation from the other driving circuit and a reverse inputvoltage.

[0009] By using the partial resonance circuit and reverse converter,drops in the flyback voltage generated when a forward converter is usedcan be avoided, and by providing the driving circuit with a delayelement, when one of the two switching elements is not driven (OFF) andthe other switching element is driven (ON), or conversely when one ofthe switching elements is driven (ON) and the other switching element isnot driven (OFF), the part at which operation of the two switchingelements overlaps can be reduced to the lowest level possible.

[0010] By constructing an arrangement wherein the reverse converter isdisposed about an iron core such that the primary side winding andsecondary side winding have differing polarities, both an insulationeffect and a reverse output effect can be obtained.

[0011] By providing a magnetic amplifier having a dead angle in thesecondary side output circuit or providing a magnetic snubber in asynchronous rectifier circuit, the outflow of the secondary side currentcan be delayed.

[0012] By connecting the primary side winding end and an earth side endof at least one of the switching elements in series via two condensershaving differing capacities and connecting a diode in parallel to thecondenser with the smaller capacity, switching loss when the switchingelements are not driven (OFF) can be reduced.

[0013] Two auxiliary windings, which are different to an output windingprovided on the secondary side of the high-frequency transformer, aredisposed on the secondary side, two synchronous rectifier drivingcircuits for transferring the output from the primary side with littleloss are connected to the two auxiliary windings respectively in a stateof differing polarities, and a switching element for the two synchronousrectifier driving circuits, which is provided with an ON-OFF signalsynchronously with the secondary voltage of the high-frequencytransformer, is provided.

[0014] An ON-OFF signal is provided to each switching element of theswitching elements for the two synchronous rectifier driving circuitssynchronously with the secondary voltage of the high-frequencytransformer. A secondary waveform from the reverse converter of thedriving circuit of the first phase of the present invention provides OFFsynchronicity with a sufficient voltage produced by the flyback energy,and thus in comparison with high-frequency diode rectification, thesecondary voltage of the high-frequency transformer has power loss onlyof the ON resistor of the switching element. Thus high efficiency can berealized.

[0015] Two resistors for determining the ON periods of the firstswitching element and second switching element are connected to a PWMcontrol circuit for outputting the driving signal so as to be parallelwhen a comparator for controlling the ON periods of the first switchingelement and second switching element is ON.

[0016] By means of such a constitution, when an input voltage isinputted or an ON signal from a remote controller is inputted, a softstart can be caused and the switching element does not attempt to risein a fully open state (rise rapidly during a short ON period), and thustransients such as an overshoot or undershoot can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic electric circuit diagram of a computer powersupply;

[0018]FIG. 2 is a view illustrating current flow when a first FET is ONand a second FET is OFF;

[0019]FIG. 3 is a view illustrating current flow when the first FET andsecond FET are both OFF;

[0020]FIG. 4 is a view illustrating current flow when the first FET isOFF and the second FET is ON;

[0021]FIG. 5 is a view showing a primary side switching circuit of thecomputer power supply;

[0022]FIG. 6 is a view illustrating a secondary side current flow whenthe first FET is ON and a fourth FET is ON;

[0023]FIG. 7 is a view illustrating the secondary side current flow whenthe first FET is OFF and a fifth FET and sixth FET are both ON; and

[0024]FIG. 8 is a time chart showing the elapse of time of a voltagewaveform and current waveform in a specified location on the primaryside and a voltage waveform on the secondary side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025]FIG. 1 shows a computer power supply which is typically providedwith a circuit for converting, for example, an AC voltage from acommercial AC power supply into a DC voltage by means of rectificationand uses the DC voltage from the circuit. To facilitate description,however, the example shown in FIG. 1 comprises a battery 1 forgenerating a DC voltage, although the present invention is not limitedthereto. The secondary side output shown in FIG. 1 is capable ofextracting three output voltages of +12V, +5V, and +3.3V, but the numberof outputs and the magnitudes of the output voltages may be set at will.

[0026] The computer power supply is constituted by a primary sideswitching circuit 2 which operates using the DC voltage of the battery 1as an input, and a secondary side output circuit 4 provided on thesecondary side of a high frequency transformer 3 for driving variousdevices of a computer using the output from the switching circuit 2 viathe high frequency transformer 3.

[0027] The primary side switching circuit 2 connects a first FET (fieldeffect transistor) Q1 serving as a first switching element and a secondFET (field effect transistor) Q2 serving as a second switching elementvia a resonance condenser 7 to the negative pole side of a primarywinding N1 provided on the primary side of the high frequencytransformer 3 in a state of opposite polarities. More specifically, thedrain side of the first FET Q1 and the cathode side of the second FET Q2are connected respectively, a first driving circuit 5 having a delayelement (a delay circuit, for example) which drives the first FET Q1 onthe basis of a driving signal is connected between the gate and cathodeof the FET Q1, and a second driving circuit 6 having a delay element (adelay circuit, for example) which drives the second FET Q2 on the basisof a driving signal is connected between the gate and cathode of thesecond FET Q2. The primary winding N1, the resonance condenser 7, andthe two FETs Q1, Q2 constitute a partial resonance circuit 8 which isresonated only when the FETs Q1, Q2 are both OFF. Note that parasiticdiodes 9, 10 are comprised in the interior of the FETs Q1, Q2respectively.

[0028] A reverse converter 11 is provided between the first drivingcircuit 5 and second driving circuit 6 for giving insulation between thetwo driving circuits 5, 6 and supplying a reverse output voltage to thesecond driving circuit 6.

[0029] The reverse converter 11 is constituted such that a primary sidewinding 11B and a secondary side winding 11A are disposed about an ironcore 11C in a state of opposite polarities, or in other words if theright side of the primary side winding 11B in the drawing is set as anegative pole, the right side of the secondary side winding 11A becomesa positive pole, and thus a flyback voltage from the primary sidewinding 11B when a third FET Q3 is OFF can be transferred to thesecondary side winding 11A in a reversed state. The third FET Q3 isprovided as a third switching element for driving the reverse converter11. The reference symbol 14 in FIG. 1 is a third driving circuit whichis connected to the gate of the third FET Q3 to drive the third FET Q3on the basis of a driving signal from a PWM control circuit 24 to bedescribed below.

[0030] By connecting the primary side winding N1 end (drain side) andthe earth (cathode) end of the first FET Q1 in series via two condensers12, 13 with differing capacitance, and connecting the condenser 12 withthe smaller capacitance in parallel with a diode 14, switching loss whenthe first FET Q1 is OFF can be reduced.

[0031] To describe the operations of the first FET Q1 and second FET Q2,when the first FET Q1 is switched ON (and the second FET Q2 with adifferent polarity is OFF) by a driving signal from the PWM controlcircuit to be described below which is outputted from the first drivingcircuit 5, a current I_(1A) flows as shown in FIG. 2. Next, when thefirst FET Q1 is switched OFF, a current I_(1B) flows along the parasiticdiode 10 as shown in FIG. 3 in order to charge the resonance condenser7. By providing the second FET Q2 such that the excitation of thehigh-frequency transformer 3 is reset by causing a flybackcounter-electromotive force of the high-frequency transformer 3 to flowinto the resonance condenser 7, switching loss when the first FET Q1 isturned OFF can be reduced. In other words, when the second FET Q2 is notprovided, the flyback voltage of the high frequency transformer 3 risesrapidly when the first FET Q1 is OFF, causing a large amount of turn-offloss which is generated during a cross when the drain current flowinginto the first FET Q1 is turned OFF. When charging of the resonancecondenser 7 is complete, the second FET Q2 switches ON (the first FET Q1remains OFF), and the energy stored in the resonance condenser 7 isdischarged such that a current I_(1C) flows as shown in FIG. 4. Whendischarge is complete, the first FET Q1 turns ON again, and theoperation described above is repeated. When the first FET Q1 switchesON, if the second FET Q2 is not provided, falling of the voltage betweenthe drain and source of the first FET Q1 is delayed, and turn-on lossincreases as the ON current of the first FET Q1 rises.

[0032] The secondary side output circuit 4 comprises four windings N2,N3, N4, and N5 disposed on the secondary side of the high frequencytransformer 3. The positive pole side of the winding N3 positioned onthe upper side of the drawing is connected via a magnetic amplifier 19Ato a high-speed rectifier diode 15 serving as a secondary siderectifying element, and thus a +12V voltage can be obtained. However, aFET or the like may be used in the flywheel side diode in order tosuppress power loss. Further, by connecting two synchronous rectifierdriving circuits 16, 17 for transferring the output from the primaryside with little loss to the winding N2 positioned third from top in astate in which the polarities of the two auxiliary windings N4, N5positioned second and fourth from top are different from one another, orin other words by connecting the first synchronous rectifier drivingcircuit 16 on the upper side to the positive pole side of the windingN4, connecting the second synchronous rectifier driving circuit 17 onthe lower side to the negative pole side of the winding N5, andproviding a fourth FET Q4 serving as a synchronous rectifier sideswitching element and a fifth FET Q5 and sixth FET Q6 serving asflywheel side switching elements, which switch ON and OFF on the basisof an output signal from the two synchronous rectifier driving circuits16, 17, a synchronous rectifier circuit is provided. When the fourth FETQ4 switches ON while the first FET Q1 is ON, +3.3V and +5V areoutputted, and when the flywheel side fifth FET Q5 and sixth FET Q6switch ON while the first FET Q1 is OFF, the three FETs Q4, Q5, and Q6are respectively connected so as to output +3.3V and +5V by thecounter-electromotive force of choke coils 18C, 18B. The referencesymbol 30 in FIG. 1 is a magnetic amplifier 19A controlling circuit forcontrolling a +12V output to a constant voltage, and the referencesymbol 20 is a magnetic amplifier 19B controlling circuit forcontrolling the +3.3V output to a constant voltage. The reference symbol21 shown in FIG. 1 is a current transformer for detecting an overcurrentwhich constitutes an overcurrent protection circuit not shown in thedrawing. As described above, a +12V output is obtained by means ofrectification using the high-speed rectifier diode 15, and thus powerloss due to the VF (forward threshold voltage) of the flywheel sidediode (high-speed rectifier diode) 15 increases. Hence, by connecting aFET which is driven by the synchronous rectifier driving circuit 17similarly to the fifth and sixth FETs Q5, Q6 in place of the flywheelside diode (high-speed rectifier diode) 15 which operates in a similarmanner to the fifth and sixth FETs Q5, Q6, power loss can be suppressedto a low level.

[0033] To describe operations of the fourth FET Q4, fifth FET Q5, andsixth FET Q6 using FIG. 6, first, the first FET Q1 is switched ON andthe current I_(1A) shown in the drawing flows into the primary sidewinding N1, whereby the output of the first synchronous rectifierdriving circuit 16 is received such that the fourth FET Q4 switches ON.As a result, a current I₁ flows so as to generate a +5V output and acurrent I₂ flows so as to generate a +3.3V output, as shown in FIG. 6.

[0034] When the first FET Q1 is switched OFF, the energy which wasaccumulated in the smoothing choke coils 18B, 18C while the first FET Q1was ON is discharged as a counter-electromotive force, and thus theoutput of the second synchronous rectifier driving circuit 17 isreceived to switch the fifth FET Q5 and sixth FET Q6 ON. As a result, acurrent I₃ flows so as to generate a +5V output and a current I₄ flowsso as to generate a +3.3V output, as shown in FIG. 7.

[0035] As shown in FIG. 1, the magnetic amplifiers 19A, 19B, each havinga dead angle, are connected to the two windings N2, N3 respectively, andthus the dead angle (also known as a conduction angle) in the T1 regionin FIG. 8 is used to delay outflow of the secondary side current suchthat loss of the ZVS (zero voltage switching) function can be prevented.Note that by using a magnetic snubber 28 in series with the +5Vrectifier FET Q4 in which a magnetic amplifier is not inserted (notswitched ON), similar effects to a case in which the magnetic amplifier19 is provided can be attained. Note that in the case of a multi-output,the two components can be used in conjunction. The reference symbol 29in FIG. 1 is a parasitic diode comprised in the interior of the fourthFET Q4.

[0036] As shown in FIG. 1, the PWM control circuit 24 is provided forgenerating a driving signal by inputting the output of a +5V constantvoltage control circuit 22 via a photocoupler 23, and two resistors R1,R2 for determining the amount of time the first FET Q1 and second FET Q2are to be ON are connected to the PWM control circuit 24 so as to beparallel when a comparator 25 for controlling the ON times of the firstFET Q1 and second FET Q2 is ON. A remote signal is inputted into thereference voltage input side of the comparator 25 via a photocoupler 26.

[0037] Typically, when an input voltage is inputted or an ON signal froma remote controller is inputted, the first FET Q1 and second FET Q2attempt to rise while fully open (the FETs are fully open during an ONperiod in order to trigger an output quickly), and thus transients suchas an overshoot or undershoot occur. By altering the ON period asdescribed above, the first FET Q1 and second FET Q2 are caused to softstart, enabling a smooth rise without the occurrence of transientsduring the output voltage rise time. The reference symbol 27 in FIG. 1is a constant current circuit.

[0038] To describe operations of the present invention using the timechart shown in FIG. 8, when a drive signal (the aforementioned drivingsignal) is outputted in a cycle T_(A), the ON period T_(a) becomesextremely narrow during dropping circuit operations and the like, asshown on the right-hand side of the drawing. Then, by ON-OFF controllingthe FETs Q1, Q2 in the driving circuits 5, 6 by means of theaforementioned drive signal, the gate voltage V_(G2) Of the second FETQ2 switches to an analogous opposite phase to the gate voltage V_(G1) ofthe first FET Q1. At this time, the rise time of the gate voltage V_(G1)of the first FET Q1 is delayed in respect of the rise time of the drivesignal by T1, and the rise time of the gate voltage V_(G2) of the secondFET Q2 is delayed in respect of falling of the drive signal by T2. Whena typical forward converter (ON/ON circuit) is used as the drivingcircuit of the second FET Q2, the drain-source voltage V_(DS3) Of thethird FET Q3 drops at a certain point, as shown in the center of thedrawing, but by using the reverse converter 11 (ON-OFF circuit)according to the present invention, the voltage can be set in asubstantially rectangular-form wave which does not drop, as shown on theright-hand side of the drawing. The reference symbol I_(D1) in FIG. 7indicates the drain current of the first FET Q1. This is indicated byI_(D) in FIG. 5. V_(T) indicates the primary side and secondary sidevoltages of the high-frequency transformer 3.

[0039] According to the first and second phase of the present invention,a partial resonance circuit and a reverse converter are used, and thusthe driving voltage (more specifically, the gate voltage VG2) can beprevented from dropping. Moreover, by providing the driving circuit witha delay element, switching loss can be reduced, and thus a computerpower supply in which efficiency is increased by at least 5% or more (tobetween 70% and 75%) compared to a conventional device using coolingfans can be provided.

[0040] According to the third phase of the present invention, a magneticamplifier having a dead angle is provided in the secondary side outputcircuit or a magnetic snubber is provided in the synchronous rectifiercircuit, and thus outflow of the secondary side current can be delayedand the loss of the ZVS (zero voltage switching) function can beprevented.

[0041] According to the fourth phase of the present invention, theprimary side winding end and an earth side end of at least one of saidswitching elements are connected in series to two condensers havingdiffering capacitance, and a diode is connected in parallel to thecondenser with the smaller capacitance, and thus switching loss when theswitching elements are not being driven (OFF) can be reduced, therebyenabling a further improvement in efficiency.

[0042] According to the fifth phase of the present invention, twoauxiliary windings which are different to an output winding provided onthe secondary side are disposed on the secondary side, two synchronousrectifier driving circuits for transferring the output from the primaryside with little loss are connected to the two auxiliary windingsrespectively in a state of differing polarities, and a switching elementfor the two synchronous rectifier driving circuits, which is providedwith an ON-OFF signal synchronously with the secondary voltage of thehigh-frequency transformer, is provided. Thus the switching elements canbe switched ON and OFF smoothly, and since the windings of thetransformer are used, synchronous timing is easy.

[0043] According to the sixth phase of the present invention, when aninput voltage is inputted or an ON signal is inputted from a remotecontroller, the switching elements can be caused to rise smoothlywithout the occurrence of transients during the rise of the outputvoltage.

What is claimed is:
 1. A computer power supply wherein a first switchingelement and a second switching element operating with a DC voltage as aninput are disposed on the primary side of a high-frequency transformer,said first switching element is connected to one end of a primary sidewinding of said high-frequency transformer, and said second switchingelement is connected to the same end of the primary side winding as theconnection side of said first switching element via a resonancecondenser and in a state of differing polarity to said first switchingelement, said primary side winding, resonance condenser, and twoswitching elements constituting a partial resonance circuit, a secondaryside output circuit for driving a load is connected to the secondaryside of said high-frequency transformer via a winding, a first drivingcircuit and a second driving circuit having a delay element are providedfor driving and halting said first switching element and secondswitching element on the basis of a driving signal by causing therespective phases thereof to differ, and a reverse converter is providedfor supplying to the input portion of one of said driving circuitsinsulation from the other of said driving circuits and a reverse inputvoltage.
 2. The computer power supply according to claim 1, wherein saidreverse converter is disposed about an iron core such that the primaryside winding and secondary side winding have differing polarities. 3.The computer power supply according to claim 1, wherein a magneticamplifier having a dead angle is provided in said secondary side outputcircuit or a magnetic snubber is provided in a synchronous rectifiercircuit.
 4. The computer power supply according to claim 1, wherein saidprimary side winding end and an earth side end of at least one of saidswitching elements are connected in series via two condensers havingdiffering capacitance, and a diode is connected in parallel to thecondenser with the smaller capacitance.
 5. The computer power supplyaccording to claim 1, wherein two auxiliary windings, which aredifferent to an output winding provided on the secondary side of saidhigh-frequency transformer, are disposed on said secondary side; twosynchronous rectifier driving circuits for transferring the output fromthe primary side to said two auxiliary windings with little loss areconnected to the two auxiliary windings respectively in a state ofdiffering polarities; and switching elements for said two synchronousrectifier driving circuits are provided, which are bestowed with anON-OFF signal synchronously with the secondary voltage of saidhigh-frequency transformer.
 6. The computer power supply according toclaim 1, wherein two resistors for determining the ON periods of saidfirst switching element and second switching element are connected to aPWM control circuit for outputting said driving signal so as to beparallel when a comparator for controlling the ON periods of said firstswitching element and second switching element is ON.